1. Field of the Invention
This invention relates generally to modularized main distributing frames located in telephone central offices and, in particular, to methods and apparatus for linking such frames with outside plant cables and central office equipment leads.
2. Description of the Prior Art
The main distributing frame (MDF) in a telephone system serves as an interface between switching equipment housed in a central office and an outside plant cable network; this interface furnishes a nonswitched interconnection juncture for joining the office equipment to the outside plant facilities. The primary function of the MDF is that of providing a point of flexibility in the telephone system where any specified one of numerous subscribers may be connected to any specified one of the many terminating points associated with the switching equipment.
Recently, the MDF has undergone significant design changes. The modern MDF systems are modularized; such systems have decreased craftsperson activity and reduced frame administration time by supplanting earlier frame systems which typically required a two-person workteam and/or cumbersome frame administration procedures. For instance, in early frame systems, interconnection between the office equipment and customer equipment was often accomplished by running long jumpers between terminal points. Once jumpers of lengths greater than twenty feet or more were installed, it became difficult to remove them when wiring changes were necessitated. This difficulty caused jumper build-up and eventual clogging of the jumper troughs.
The modular systems have been designed primarily to alleviate jumper congestion. To achieve short jumper arrangements, the outside plant cables are uniformly distributed over many, diverse frame appearances. In modern MDF designs, this distribution is typically accomplished with so-called tip cables that couple the cables located in a cable entrance facility, typically the cable vault, with the MDF. In order to improve transmission performance on the facilities, the tip cables are shielded and have an increased cable diameter resulting in a many-fold increase in cable volume over more conventional MDF systems. The potential for severe cable congestion in the overhead racking in central offices due to pile-ups and cross-overs required a new approach to MDF cable routing in order to implement MDF systems that minimize jumper congestion.